Re: [Xen-devel] [PATCH] Fix boot crash on xsm/flask enabled builds when no policy module is present

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 26/08/2013 13:24, Tomasz Wroblewski wrote:
> On 08/26/2013 01:12 PM, Jan Beulich wrote:
>>>>> On 26.08.13 at 12:03, Tomasz
>>>>> Wroblewski<tomasz.wroblewski@xxxxxxxxxx>  wrote:
>>> Xen crashes on boot of xsm/flask enabled builds, if policy module is
>>> not
>>> specified.
>>> This seems to have worked on 4.1 at least.
>> Looking at the code (4.1.5) I can't see what would prevent the
>> same NULL pointer deref. Care to explain?
> The crash doesn't happen at the NULL pointer dereference site though,
> but a bit later, when xen tries to flush tlbs for first time I
> believe, which happens during page allocation for the initial domain
> structure. I traced it to the following ASSERT in smp.c (so yes I
> should add this particular crash likely is limited to debug builds then)
>
> void flush_area_mask(const cpumask_t *mask, const void *va, unsigned
> int flags)
> {
>     ASSERT(local_irq_is_enabled());
>     ...
>
> The actual crash message is unhelpful since it's basically only
>
> ...
> (XEN) Using scheduler: SMP Credit Scheduler (credit)
> (XEN) Unknown interrupt (cr2=0000000000000000)
>
>
> Either removing the assert (which is obviously bad), or checking for
> the null pointer deref as in the submitted patch seems to be fixing
> it. I'm suspecting it was always broken somehow but just was hidden or
> had different side effects on 4.1 than it does now. I do lack for a
> good explanation why fiddling with null addresses breaks up this
> assert, though.

Do you have any more information than that?  Stack trace or even a stack
dump?

I cant spot how those two would be connected.

~Andrew

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